Semiconductor light-emitting element

ABSTRACT

A semiconductor light-emitting element includes, a first semiconductor layer, a second semiconductor layer, a light-emitting layer provided between the first semiconductor layer and the second semiconductor layer, a first electrode connected to the first semiconductor layer, and a second electrode provided on the second semiconductor layer. A side of the second electrode facing to the second semiconductor layer is composed of at least any one of silver and silver alloy. The second electrode has a void having a width of emission wavelength or less of the light-emitting layer in a plane of the second electrode facing to the second semiconductor layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2008-062611, filed on Mar. 12,2008; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a semiconductor light-emitting element and amethod for producing the same.

2. Background Art

For improving brightness of a semiconductor light-emitting element,improvement of light taking-out efficiency is important. In asemiconductor light-emitting element, as one example of a structure inwhich high heat release property and high light taking-out efficiencycan be expected, there is a flip-chip type structure in which alight-emitting layer side of a wafer is contacted with a heatsink sideand the emitted light is taken out from the substrate side directly orwith reflected by the reflection film.

The light emitted in the semiconductor light-emitting element changesits light pathway according to the incident angle to the interfacehaving difference in refractive index. When the incident angle is such adeep incident angle as being near perpendicular to the interface, thelight is taken out of the semiconductor element, and when a shallowincident angle, the light is totally internally reflected and returns tothe inside of the semiconductor light-emitting element.

In the case of the flip-chip type semiconductor light-emitting element,for improving the light taking-out efficiency, it is thought that thelight taking-out surface of the substrate is processed to be a domeshape and that nano-convex-concave structure having diffraction functionis formed. However, for example, in the case of a semiconductorlight-emitting element in which nitride semiconductor is formed on asapphire substrate, refractive index difference between the substrateand the semiconductor layer is large, and therefore, in this structure,the light emitted in the semiconductor layer is reflected by itsinterface and easily trapped in the semiconductor layer. Therefore, evenif the light taking-out surface of the substrate is devised, there is aroom for upgrading improvement of the light taking-out efficiency.

For improving the light taking-out efficiency, it is also thought thatthe convex-concave structure is formed by processing the substratesurface on which the semiconductor layer is formed or by forming anon-flat layer in the semiconductor layer or by processing the surfaceof the semiconductor layer on which a reflective film will be formed.However, every method thereof requires advanced techniques, andadditionally, these methods could leads to that the crystal growthcondition for forming the convex-concave structure and the crystalgrowth condition for improving characteristic of the semiconductorlight-emitting element are not highly compatible. That is, by formingthe convex-concave structure, the crystal quality is degraded, andthereby, degradation of electric characteristic or optic characteristicis feared.

In JP-A 2007-5591 (Kokai), there has been proposed a structure in whichthe electrode combining with a function of a high efficient reflectivefilm has a region having a width of ½ or less of a wavelength of theradiation light from the light-emitting layer.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided asemiconductor light-emitting element including: a first semiconductorlayer; a second semiconductor layer; a light-emitting layer providedbetween the first semiconductor layer and the second semiconductorlayer; a first electrode connected to the first semiconductor layer; anda second electrode provided on the second semiconductor layer; a side ofthe second electrode facing to the second semiconductor layer beingcomposed of at least any one of silver and silver alloy, and the secondelectrode having a void having a width of emission wavelength or less ofthe light-emitting layer in a plane of the second electrode facing tothe second semiconductor layer According to another aspect of theinvention, there is provided a method for producing a semiconductorlight-emitting element including, a first semiconductor layer, a secondsemiconductor layer, and a light-emitting layer provided between thefirst semiconductor layer and the second semiconductor layer, a firstelectrode connected to the first semiconductor layer, and a secondelectrode provided on the second semiconductor, a side of the secondelectrode facing to the second semiconductor layer being composed of atleast any one of silver and silver alloy, including: forming aconductive film to be the second electrode on the second semiconductorlayer; attaching at least any one of water and an ionized substance tothe conductive film; and forming a void having a width of emissionwavelength or less of the light-emitting layer in at least a plane ofthe conductive film facing to the second semiconductor layer byheat-treating the conductive film being configured to make a gap betweengrain boundaries in the conductive film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic views illustrating a structure of asemiconductor light-emitting element according to a first embodiment ofthis invention;

FIG. 2 is an enlarged schematic view illustrating a structure of asubstantial part of the semiconductor light-emitting element accordingto the first embodiment of this invention;

FIGS. 3A and 3B are schematic views illustrating voids of thesemiconductor light-emitting element according to the first embodimentof this invention;

FIG. 4 is a sectional schematic view illustrating a structure of thesemiconductor light-emitting element according to the first example.

FIG. 5 is a flow chart illustrating a method for producing asemiconductor light-emitting element according to a second embodiment ofthis invention.

FIGS. 6A to 6C are schematic sectional views following step sequenceillustrating a part of the method for producing a semiconductorlight-emitting element according to the second example.

FIGS. 7A to 7D are schematic sectional views following the step sequenceof the substantial part illustrating the method for producing asemiconductor light-emitting element according to the second example.

FIGS. 8A to 8D are schematic sectional views following the step sequencefollowing FIGS. 7A to 7D.

FIG. 9 is a schematic view showing behavior of crystal grain in heattreatment in the method for producing a semiconductor light-emittingelement according to the second example.

FIG. 10 is a sectional schematic view illustrating a structure of thesemiconductor light-emitting element of the first comparative example.

FIGS. 11A to 11E are schematic views following the steps illustratingthe method for producing the semiconductor light-emitting element of thefirst comparative example.

FIGS. 12A and 12B are scanning electron micrographs illustrating thestructures of the surfaces of the second electrodes according to thefirst example and the first comparative example.

FIG. 13 is a sectional schematic view illustrating a structure of thesemiconductor light-emitting element according to a third embodiment ofthis invention.

FIGS. 14A to 14G are schematic sectional views following step sequenceof the substantial part illustrating the method for producing asemiconductor light-emitting element according to the third example.

FIG. 15 is a scanning electron micrograph illustrating the structure ofthe surface of the second electrode of the semiconductor light-emittingelement according to the third example.

FIG. 16 is a graphic view illustrating the relation between the heattreatment temperature in the semiconductor light-emitting elementaccording to the third example and the area ratio of the void of theelement.

FIG. 17 is a graphic view illustrating the relation between the heattreatment temperature and the optical output of the element according tothe third example.

FIGS. 18A to 18E are schematic sectional views following step sequenceof the substantial part illustrating the method for producing asemiconductor light-emitting element of the second comparative example.

FIGS. 19A to 19E are schematic sectional views following step sequenceof the substantial part illustrating the method for producing asemiconductor light-emitting element of the second comparative example.

FIGS. 20A and 20B are scanning electron micrographs illustratingstructures of the surfaces of the second electrodes of the semiconductorlight-emitting elements of the second and third comparative examples.

FIG. 21 is a scanning electron micrograph illustrating structure of thesurface of the second electrode of the semiconductor light-emittingelement of the fourth example.

FIG. 22 is a sectional schematic view illustrating the structure of thesemiconductor light-emitting element according to the fourth embodimentof this invention.

FIGS. 23A to 23G are schematic sectional views following step sequenceof the substantial part illustrating the method for producing asemiconductor light-emitting element according to the fourth example.

FIGS. 24A and 24B are schematic views illustrating a structure of thesemiconductor light-emitting element according to the fifth embodimentof this invention.

FIG. 25 is a sectional schematic view illustrating a structure of thesemiconductor light-emitting element according to a sixth embodiment ofthis invention.

FIG. 26 is a sectional schematic view illustrating another structure ofthe semiconductor light-emitting element according to a sixth embodimentof this invention.

FIG. 27 is a sectional schematic view illustrating a structure of thesemiconductor light-emitting element according to the seventh embodimentof this invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will now be described in detail withreference to the drawings.

It is noted that the figures are schematic or conceptual. Therelationship between the thickness and the width of various portions andthe ratio in size between the portions are not necessarily the same asthose in reality. Furthermore, the same portion may be shown differentlyin dimension and ratio in different figures.

In the specification and the associated drawings, the same components asthose described previously with reference to earlier figures are labeledwith like reference numerals, and the detailed description thereof isomitted as appropriate.

First Embodiment

FIGS. 1A and 1B are schematic views illustrating a structure of asemiconductor light-emitting element according to a first embodiment ofthis invention.

That is, FIG. 1B is a plan schematic view illustrating a structure ofthe semiconductor light-emitting element according to a first embodimentof this invention, and FIG. 1A is a schematic view of the A-A′ linesection.

As shown in FIGS. 1A and 1B, the semiconductor light-emitting element 10according to the first embodiment of this invention has a firstsemiconductor layer 120, a second semiconductor layer 140, alight-emitting layer 130 provided between the first semiconductor layer120 and the second semiconductor layer 140, and a first electrode 160provided on the first semiconductor layer 120, and a second electrode150 provided on the second semiconductor layer 140.

That is, the semiconductor light-emitting element 10 according to thisembodiment has a semiconductor layer 148 including the firstsemiconductor layer 120, the second semiconductor layer 140, and thelight-emitting layer 130 sandwiched thereby. For this semiconductorlayer 148, a nitride semiconductor such as Al_(x)Ga_(1−x−y)In_(y)N (x≧0,y≧0, x+y≦1) can be used. However, this invention is not limited thereto.

And, for the first semiconductor layer 120, semiconductor having n-typeconductivity can be used, and for the second semiconductor layer 140,semiconductor having p-type conductivity can be used.

Moreover, as shown in FIGS. 1A and 1B, the semiconductor layers (thefirst semiconductor layer 120, the light-emitting layer 130, and thesecond semiconductor layer 140) can be formed on a substrate 110. Inthis case, the method for forming the semiconductor layer 148 is notparticularly limited, and a technique such as a metal organic chemicalvapor deposition method and a molecular-beam epitaxial growth method canbe used.

For this substrate 110, for example, sapphire, SiC, GaN, GaAs, Si, orthe like can be used. In the case of using such a material oftransmitting light emitted from the light-emitting layer 130 assapphire, light can be taken out through the substrate 110. On the otherhand, when the substrate 110 is formed by a material that does nottransmit light emitted from the light-emitting layer 130, the light canalso be taken out to the outside with reflected by the interface betweenthe semiconductor layer 148 and the substrate 110. The substrate 110 maybe removed on the way of the production of the semiconductorlight-emitting element or after the production thereof. In this case,the light emitted from the light-emitting layer 130 can be taken outfrom the lower surface of the semiconductor layer 148 (the surface ofthe lower side in FIG. 1A).

And, for the second electrode 150, for example, at least any one ofsilver and silver alloy can be used. However, this invention is notlimited thereto, and in the second electrode 150, at least the sidefacing to the second semiconductor layer 140 may be made of at least anyone of silver and silver alloy.

A material of a conductive film to be the second electrode 150 may be asilver monolayer film or a silver alloy layer consisting of silver andmetal except for silver. The reflection efficiencies of many metalmonolayer films except for silver tend to decrease as the wavelength isshorter in the ultraviolet spectrum, but silver also has high reflectionefficiency characteristic with respect to light of the ultravioletspectrum of 370 nm to 400 nm. Therefore, by using silver or silver alloyas the second electrode 150, the light generated in the light-emittinglayer 130, particularly light of ultraviolet spectrum is reflectedhigh-efficiently, and the semiconductor light-emitting element 10 ofhigh brightness can be realized.

And, in the semiconductor light-emitting element of ultravioletemission, when the conductive film to be the second electrode 150 isformed by silver alloy, it is preferable that the second semiconductorlayer 140 side of the conductive film has a higher component ratio ofsilver than that of the other parts. It is preferable that the thicknessof the conductive film to be the second electrode 150 is thicker than aninverse number of an absorption coefficient of silver for ensuring thereflection efficiency to light, and 100 nm or more is furtherpreferable.

Furthermore, the second electrode 150 has a void 210 having a width ofemission wavelength or less of the light-emitting layer 130 in a planeof the second electrode facing to the second semiconductor layer.

As described later, by the void 210, the light pathway of the lightemitted in the light-emitting layer 130 can be changed, the lighttrapping effect is suppressed by total internal reflection, and thesemiconductor light-emitting element having high light taking-outefficiency can be provided.

Moreover, it is sufficient that the void 210 is provided at least in theinterface side of the electrode 150 to the second semiconductor layer140, and the void 210 may also be provided in the interface of thesecond electrode 150 opposite to the second semiconductor layer 140 atthe same time of being provided in the interface side of the electrode150 to the second semiconductor layer 140. Moreover, the void 210 mayalso be provided in the layer of the second electrode 150 at the sametime of being provided in the interface side of the electrode 150 to thesecond semiconductor layer 140, and furthermore, the void 210 may beprovided so as to pass through the thickness direction of the secondelectrode 150. That is, it is sufficient that the void 210 is providedat least in the interface side of the electrode 150 to the secondsemiconductor layer 140, to which the light from the semiconductor layer148 is incident.

The void 210 of the second electrode 150 can be formed by self-assemblyaccording to migration of silver by high-temperature heat treatment.

For the material of the first electrode 160, various monolayer films ormultilayer films with conductivity that can be used as the ohmicelectrode of the first semiconductor layer 120 can be used as thematerial of the first electrode 160. The method for forming the firstelectrode 160 is not particularly limited, but for example, it ispossible that the multilayer structure is formed by an electron-beamdeposition method and then sintering treatment is performed. In the caseof performing the sintering treatment, it is preferable that a pad isprovided separately in the first electrode 160 for improvingbondability.

In order to improve bondability of wire bonding, to improve die shearstrength in formation of gold bump with a ball bonder, to performapplication to flip-chip mount, and so forth, a pad may be separatelyprovided in the second electrode 150. The film thickness of the pad canbe selected, for example, in 100 nm to 10000 nm.

FIG. 2 is an enlarged schematic view illustrating a structure of asubstantial part of the semiconductor light-emitting element accordingto the first embodiment of this invention.

As shown in FIG. 2, in the semiconductor light-emitting element 10according to the first embodiment of this invention, the light incidentto the part except for the void 210 of the light emitted from thelight-emitting layer 130 to the second electrode 150 is mirror-reflectedaccording to geometric optics similarly to the light L. On the otherhand, because the width of the void 210 is smaller than the emissionwavelength, the light incident to the void 210 shows behavior explainedby wave optics such as scattering or diffraction. As a result, forexample, lights X1, X2, and X3 scatter-reflected are generated.

As described above, in the semiconductor light-emitting element 10according to this embodiment, by providing the void 210 having a widthof wavelength or less in the second electrode 150, the region of scattercharacteristic (diffuse reflection characteristic) can be formed in theinterface between the second electrode 150 and the second semiconductorlayer 140. Thereby, lights having various angles (such as light X1, X2,and X3) are generated, the incident angle of a part of the light thathas a shallow incident angle with respect to the interface withrefractive index difference (such as the interface between thesemiconductor layer 148 and the substrate) and that is trapped insidethe semiconductor light-emitting element 10 can be changed, and thelight can be effectively taken out to the outside.

Thereby, by the semiconductor light-emitting element 10 according tothis embodiment, a semiconductor light-emitting element with high lighttaking-out efficiency can be provided.

In general, as the width of the void 210 becomes smaller than theemission wavelength, wave property of the light is enhanced and thescatter-reflected component of the light increases. As a result thereof,the light taking-out efficiency of the semiconductor light-emittingelement 10 is improved.

Here, “mirror reflection” is reflection that the incident angle and thereflection angle of the light are equal as explained by geometricoptics, “diffuse reflection” is reflection that the light is scatteredto all of the directions as explained by wave optics.

In the case of the semiconductor light-emitting element in which asapphire substrate is used, the reflective index difference between thesubstrate 110 and the semiconductor layer 148 is large, and therefore, alarge part of the emitted light are reflected on the interface and alarge part of the emitted light is easily trapped inside thesemiconductor layer 148. By contrast, according to the semiconductorlight-emitting element 10 according to this embodiment, bydiffuse-reflecting the emitted light, the light can be effectively takenout to the outside, and therefore, the light taking-out efficiency isimproved. As described above, it is effective to apply the semiconductorlight-emitting element 10 according to this embodiment to thesemiconductor light-emitting element in which a sapphire substrate isused.

FIGS. 3A and 3B are schematic views illustrating voids of thesemiconductor light-emitting element according to the first embodimentof this invention.

That is, the FIGS. 3A and 3B illustrate size (width) of voids when thevoids have an elliptical shape and a shape except for elliptical shape,respectively.

As shown in FIGS. 3A and 3B, in the semiconductor light-emitting element10 according to the first embodiment, the width of the void 210represents the long diameter S in the case that the sectional shape ofthe void 210 in the interface of the void 210 to the secondsemiconductor layer 140 is an elliptical shape (FIG. 3A), and the widthof the void 210 represents the longest direct distance T in the void 210in the other cases (FIG. 3B).

And, the width of the void 210 becomes the above-described long diameterS or the direct distance T in the plane shape of the void 210 in thesection of the plane of the second electrode 150 facing to the secondsemiconductor layer 140.

It is preferable that the width of the void 210 is the emissionwavelength or less. The emission spectrum of the semiconductorlight-emitting element 10 has a half bandwidth of about several tens ofnanometers. However, the emission wavelength represents the peakemission wavelength when the optical output becomes the maximum in thedefault operating current.

When an action body such as the void 210 is sufficiently larger incomparison to the wavelength of the light, the light is treated as alight flux going straight and the behavior of the light is explained bygeometric optics such as Snell's law. On the other hand, when the actionbody has approximately the same size as the wavelength of the light, thelight increases its wave property, and phenomenon that cannot beexplained by geometric optics is generated. Bending of the light iscaused by the wave property such as diffraction or scattering. The waveproperty significantly appears in the region in which the size of theaction body is the wavelength or less. In this region, the behavior ofthe light cannot be strictly calculated based on electromagnetics.

In a general semiconductor light-emitting element, there are methods inwhich for improving the light taking-out efficiency, non-flat surfaces(convex-concave structure) are formed by processing, a substratesurface, inside of a semiconductor layer, and a surface of thesemiconductor layer in contact with a reflection film. However, thesurfaces formed by these methods have convex-concave structures withlarger characters than the wavelength of the light and havemirror-reflection characteristics according to the geometric optics asviewed microscopically. By contrast, in the semiconductor light-emittingelement 10 according to this embodiment, the size of the void 210 iswavelength of the light or less, and has a characteristic of the waveproperty which cannot be explained by geometrical optics as describedabove. Thereby, the semiconductor light-emitting element with high lighttaking-out efficiency that cannot be obtained by the other methods canbe provided.

As the density or the area ratio of the void 210 in the interface of thesecond electrode 150 to the second semiconductor layer 140 is higher,the light taking-out efficiency is higher. However, when the density andthe area ratio of the void 210 becomes too high, the contact areabetween the second electrode 150 and the second semiconductor layer 140becomes small and the operation voltage occasionally becomes high.

In this case, in such a case of lateral direction current application asthe second electrode 150 and the first electrode 160 are onapproximately the same plane like the semiconductor light-emittingelement 10 illustrated in FIGS. 1A and 1B, current tends to concentratein the region in which the distance between the second electrode 150 andthe first electrode 160 become the minimum, and therefore, decreasingthe contact area between the second electrode 150 and the secondsemiconductor layer 140 due to the void 210 does not act on theoperation voltage to the extent of the lowering amount.

Considering the combination with operation voltage, it is preferablethat the area ratio of the void 210 with respect to the entire area ofthe second electrode 150 is 10% or less, and 5% or less is furtherpreferable. Moreover, in the case of providing a plurality of voids 210in the second electrodes 150, it is desirable that the widths of themajority of these voids 210 are set to be wavelength or less of theemitted light. Thereby, more than half of the voids 210 generatediffraction or scattering based on the wave property of the light asdescribed above, and the light taking-out efficiency can be improved.Moreover, when a plurality of voids 210 are provided in the secondelectrode 150, it is also possible that the average of the widths ofthese voids 210 is set to be wavelength of the emitted light or less.Thereby, also, a large number of the voids generate diffraction orscattering based on the wave property of the light, and the lighttaking-out efficiency can be improved.

FIRST EXAMPLE

Hereinafter, a first example according to this embodiment will beexplained.

FIG. 4 is a sectional schematic view illustrating a structure of thesemiconductor light-emitting element according to the first example ofthis invention.

As shown in FIG. 4, a semiconductor light-emitting element 11 accordingto the first example of this invention has the same structure as thesemiconductor light-emitting element 10 according to the firstembodiment illustrated in FIGS. 1A and 1B.

The planar structure thereof can be the same as the semiconductorlight-emitting element 10 according to this embodiment illustrated inFIGS. 1A and 1B, and therefore, the explanation thereof will be omitted.

The semiconductor light-emitting element 11 according to this examplehas the semiconductor layer 148 in which on the substrate 110, a firstAlN buffer layer 122 with a film thickness of 3 nm to 20 nm and a highcarbon concentration (the carbon concentration is 3×10¹⁸ cm⁻³ to 5×10²⁰cm⁻³), a second AlN buffer layer 123 of high purity with a filmthickness of 2 μm (the carbon concentration is 1×10¹⁶ cm⁻³ to 3×10¹⁸cm⁻³), a non-doped GaN buffer layer 124 with a film thickness of 3 μm, aSi-doped n-type GaN contact layer 125 with a film thickness of 4 μm (theSi concentration is 1×10¹⁶ cm⁻³ to 1×10¹⁹ cm⁻³ ), a Si-doped n-typeAlGaN clad layer 126 with a film thickness of 0.02 μm (the Siconcentration is 1×10¹⁶ cm⁻³), the light-emitting layer 130 with a filmthickness of 0.075 μm having a multiquantum well structure in whichSi-doped n-type AlGaN barrier layers (the Si concentration is 1×10¹⁹cm⁻³) and GaInN light-emitting layers (peak emission wavelength inapplying current is 380 nm) are stacked alternately in three periods, anon-doped AlGaN spacer layer 142 with a film thickness of 0.02 μm, aMg-doped p-type AlGaN clad layer 143 with a film thickness of 0.02 μm(the Mg concentration is 1×10¹⁹ cm⁻³), a Mg-doped p-type GaN contactlayer 144 with a film thickness of 0.1 μm (the Mg concentration is1×10¹⁹ cm⁻³), and a high-concentration-Mg-doped p-type GaN contact layer145 with a film thickness of 0.02 μm (the Mg concentration is 2×10²⁰cm⁻³) are stacked.

And, the semiconductor light-emitting element 11 has the secondelectrode (p-side electrode) 150 provided with a void having a width ofwavelength of the light or less.

Thereby, the semiconductor light-emitting element with high lighttaking-out efficiency can be provided.

As described above, the first AlN buffer layer 122, the second AlNbuffer 123, the non-doped GaN buffer layer 124, the Si-doped n-type GaNcontact layer 125, and the Si-doped n-type AlGaN clad layer 126 becomethe first semiconductor layer 120.

And, the non-doped AlGaN spacer layer 142, the Mg-doped p-type AlGaNclad layer 143, the Mg-doped p-type GaN contact layer 144, and thehigh-concentration-Mg-doped p-type GaN contact layer 145 become thesecond semiconductor layer 140.

The Mg-doped p-type GaN contact layer 144 and thehigh-concentration-Mg-doped p-type GaN contact layer 145 become a p-typeGaN contact layer 146.

The first AlN buffer layer 122 with a high carbon concentrationfunctions to relax the mismatch of the lattice to the substrate 110, andparticularly, reduces screw dislocation.

The second AlN buffer layer 123 of high purity is a layer forplanarizing the surface at the atomic level and reducing defects of thenon-doped GaN buffer layer to be grown thereon, and it is preferablethat the thickness thereof is thicker than 1 μm. Moreover, forpreventing warpage due to strain, it is desirable that the thickness is4 μm or less. The second AlN buffer layer of high purity is not limitedto AlN, but Al_(x)Ga_(1−x)N (0.8≦x≦1) is possible, the warpage of thewafer can be compensated.

The non-doped GaN buffer layer 124 functions as defect reduction by3-dimentional island growth on the second AlN buffer layer 123. For theplanarization of the growth surface, it is necessary that the averagefilm thickness of the non-doped GaN buffer layer 124 is 2 μm or more.Moreover, from the viewpoints of reproducibility and lowering ofwarpage, it is appropriate that the total film thickness of thenon-doped GaN buffer layer 124 is 4 to 10 μm.

By adopting these buffer layers, in comparison to a conventionallow-temperature growth AlN buffer layer, it can be realized that thedefects are reduced to about 1/10. By this technique, despitehigh-concentration Si-doping to the n-type GaN contact layer (Si dopedn-type GaN contact layer) 125 and emission of ultraviolet spectrum, thesemiconductor light-emitting element with high efficiency can beproduced.

That is, in the case of a general nitride semiconductor layer formed ona sapphire substrate, a large number of defects existing in thesemiconductor layer 148 and the low-temperature growth buffer layerbecoming amorphous or polycrystalline and so forth are light absorbers,and the light is absorbed in being reflected, and therefore, loss of thelight is caused.

At this time, by using the single crystal AlN buffer layer (the firstAlN buffer layer 122, the second AlN buffer layer 123 of high purity,and the non-doped GaN buffer layer 124) like the semiconductorlight-emitting element 11 according to this example, not only absorptionin the buffer layer becomes difficult to be caused but also the defectsin the semiconductor layer 148 is reduced, and therefore, factorscausing light absorption in the semiconductor layer 148 can be reducedas much as possible, and the loss can be lowered. Therefore, by usingthe single crystal AlN buffer layer, even if density and area ratio ofthe voids 210 is lowered, high light taking-out efficiency can beobtained.

As described above, in the semiconductor light-emitting element of thisexample, the second electrode (p-side electrode) 150 provided with thevoid 210 having a width of wavelength of the light or less is used, andalso, the single crystal AlN buffer layer is used, and therefore,absorption is difficult to be caused in the buffer layer, and thedefects in the semiconductor layer decreases, and the factors causinglight absorption in the semiconductor layer can be reduced as much aspossible, and the semiconductor light-emitting element with high lighttaking-out efficiency can be provided.

In the semiconductor light-emitting element 11 of this example, if Mgconcentration of the high-concentration-Mg-doped p-type GaN contactlayer 145 is set to be at a level of 10²⁰ cm⁻³, which is relativelyhigh, ohmic property between the p-type GaN contact layer 146 and thesecond electrode 150 is improved. However, in the case of asemiconductor light-emitting diode, differently from semiconductor laserdiode, the distance between the high-concentration-Mg-doped p-type GaNcontact layer 145 and the light-emitting layer 130 is small, andtherefore, if the Mg concentration of the high-concentration-Mg-dopedp-type GaN contact layer 145 is set to be high as described above,degradation of characteristics due to Mg diffusion is feared. However,in the case of the semiconductor light-emitting diode, current densityin the operation is low, and therefore, by suppressing the Mgconcentration to be 10¹⁹ cm⁻³, the diffusion of Mg can be preventedwithout largely degrading the electric characteristics, and thelight-emitting characteristics can be improved.

Moreover, by using the single crystal AlN buffer layer, differently fromthe low-temperature growth AlN buffer layer that is amorphous orpolycrystalline, the buffer layer is difficult to become an absorbingbody to the emitted light, and the defects in the semiconductor layer148 can be reduced, and the factors causing light absorption in thesemiconductor layer 148 can be reduced as much as possible. Thereby, theemitted light can repeat reflection at many times in the interface ofthe substrate 110 and the epitaxial layer and in the interface of theepitaxial layer and the p-side electrode 150, and therefore, the emittedlight is trapped in the epitaxial layer and becomes easy to be affectedby the void 210, and thereby, even if the density and the area ratio ofthe void 210 is low, high effect can be obtained.

Second Embodiment

Next, a method for producing a semiconductor light-emitting elementaccording to a second embodiment of this invention will be explained.

FIG. 5 is a flow chart illustrating a method for producing asemiconductor light-emitting element according to a second embodiment ofthis invention.

As shown in FIG. 5, in the method for producing a semiconductorlight-emitting element according to the second embodiment of thisinvention, first on the semiconductor layer 148, a conductive film to bethe second electrode (p-side electrode) 150 is formed (Step S110). Thisconductive film can include at least any one layer of silver and silveralloy.

And, to this conductive film, at least any one of water and ionizedsubstance is attached (Step S120).

And, the void 210 having a width of emission wavelength or less of theemitting light of the semiconductor light-emitting element in at least aplane of the conductive film facing to the second semiconductor layer140 by heat-treating the conductive film at a high temperature to make agap in grain boundaries in the conductive film (Step S130).

As described above, according to the method for producing thesemiconductor light-emitting element of this embodiment, by making theconductive film to be the second electrode 150 migrate, a gap is made ingrain boundaries in the conductive film, the void 210 having a width ofwavelength or less of the emitted light can be easily formed in theconductive film like self-assembly, and the producing method by whichthe semiconductor light-emitting element with high light taking-outefficiency can be easily produced.

As described later, before forming the above-described conductive filmto be the second electrode 150, a drying step for removing moistureattached to the surface of the semiconductor layer 148 and so forth canbe provided. Moreover, as described later, by controlling temperaturecondition of the above-described high-temperature heat treatment and thetemperature-lowering rate after the high-temperature heat treatment,generation of the void 210 can be controlled.

SECOND EXAMPLE

Hereinafter, the method for producing a semiconductor light-emittingelement that is a second example according to this embodiment will beexplained. That is, the second example is an example of theabove-described method for producing the semiconductor light-emittingelement 11 according to the first example.

FIGS. 6A to 6C are schematic sectional views following step sequenceillustrating a part of the method for producing a semiconductorlight-emitting element according to the second example of thisinvention.

FIG. 6A is a view of a first step, and FIGS. 6B and 6C are viewsfollowing the preceding views, respectively.

As shown in FIG. 6A, in the method for producing the semiconductorlight-emitting element 11 according to the second example of thisinvention, first by using a metal organic chemical vapor deposition, onthe substrate 110 whose surface is composed of sapphire c surface, thefirst AlN buffer layer 122 with high carbon concentration, the secondAlN buffer layer 123 of high purity, the non-doped GaN buffer layer 124,the Si-doped n-type GaN contact layer 125, the Si-doped n-type AlGaNclad layer 126, the light-emitting layer 130 having a multiquantum wellstructure in which Si-doped n-type AlGaN barrier layers and GaInNlight-emitting layers are stacked alternately in three periods, thenon-doped AlGaN spacer layer 142, the Mg-doped p-type AlGaN clad layer143, the Mg-doped p-type GaN contact layer 144, and thehigh-concentration-Mg-doped p-type GaN contact layer 145 were stacked inthis order. Film thicknesses and concentrations of carbon, Si, and Mgare the same as described in the first example.

And, as shown in FIG. 6B, in some region of the semiconductor layer 148,the p-type semiconductor layer (second semiconductor layer) 140 and thelight-emitting layer 130 and the Si doped n-type AlGaN clad layer 126were removed by dry etching by using a mask until the n-type contactlayer 125 is exposed to the surface thereof.

And, as shown in FIG. 6C, on the entire the semiconductor layer 148containing a part of the exposed n-type semiconductor layer (firstsemiconductor layer) 140, SiO₂ film 310 is stacked at a film thicknessof 400 nm by using a thermal CVD (Chemical Vapor Deposition) apparatus.

And, the p-side electrode 150 is formed thereon. Hereinafter, the methodfor forming this p-side electrode 150 will be explained in detail. Thatis, hereinafter, only the region 300 shown in FIG. 6C in which thep-side electrode 150 is formed will be explained.

FIGS. 7A to 7D are schematic sectional views following the step sequenceof the substantial part illustrating the method for producing asemiconductor light-emitting element according to the second example ofthis invention.

FIG. 7A is a view of a first step, and FIGS. 7B, 7C, and 7C are viewsfollowing the preceding views, respectively.

And, FIGS. 8A to 8D are schematic sectional views following the stepsequence following FIGS. 7A to 7D.

FIG. 7A is an enlarged schematic sectional view of the region 300illustrated in FIG. 6C in which the SiO₂ film 310 is formed on thesemiconductor layer.

First, as shown in FIG. 7B, on the semiconductor layer 148, a lift-offresist 320 is formed in a predetermined pattern, and some of the SiO₂film 310 on the p-type GaN contact layer 146 was removed by ammoniumfluoride treatment, and moisture on the wafer (the substrate 110, thesemiconductor layer 148, and the SiO₂ film 310 in this case) was blownoff by an air blow or a spin dryer or the like.

In this case, as shown in FIG. 7C, in the state that the moisture on thewafer is merely blown off, a little moisture remains on the wafersurface in the state of being not controlled.

Therefore, then, as shown in FIG. 7D, the moisture on the wafer issufficiently dried and removed.

And, as shown in FIG. 8A, by a vacuum deposition apparatus, on theentire wafer, silver (Ag), platinum (Pt), and titanium (Ti) werefilm-formed in this order at a total film-thickness of 200 nm, andthereby, a conductive film 151 for forming the p-side electrode 150 wasformed. This invention is not limited thereto, and for this conductivefilm 151, at least any one layer of silver and silver alloy can be used.

And, as shown in FIG. 8B, the resist 320 was dissolved by an organicsolvent, and thereby, only the conductive film 151 formed on the resist320 was removed and sufficiently rinsed by ultrapure water, and then,the wafer was sufficiently dried on a hot plate at 120° C. Thereby, thep-side electrode 150 was formed in the region in which the SiO₂ film 310was removed.

And, as shown in FIG. 8C, the wafer was kept in a clean room in whichthe temperature and the humidity were controlled to be 25° C.±1° C. and50%±1% respectively for 24 hours, and thereby, a little water (moisture)330 and/or ionized substance 340 was attached to the surface of theformed p-side electrode 150.

And, as shown in FIG. 8D, by using an RTA (Rapid Thermal Annealing)apparatus, temperature of the wafer was raised to 800° C. at 5°C./second in a nitrogen atmosphere, and the wafer was subjected to heattreatment for 1 minute in the nitrogen atmosphere at 800° C., and thetemperature was lowered to the normal temperature at 0.5° C./second, andthereby, the void 210 was formed in the interface between the p-type GaNcontact layer 146 and the p-side electrode 150. That is, migration wasgenerated in the conductive film 151, and a gap was made between thegain boundaries of the conductive film 151, and thereby, the void 210could be formed.

Then, for forming the first electrode (n-side electrode) 160, apatterned lift-off resist (not shown) was formed, the SiO₂ film 310 onthe n-type contact layer 125 exposed from the resist was removed byammonium fluoride treatment.

And, by a vacuum deposition apparatus, a thin film composed of Ti/Pt/Auwas formed on the entire wafer at the film thickness of 500 nm, and bylift-off method, in the region in which the SiO₂ film 310 was removed,the n-side electrode 160 wafer was formed.

Then, the back surface of the substrate 110 was polished, and the waferwas cut by cleavage or diamond blade, and thereby the semiconductorlight-emitting element could be formed.

As described above, in the method for producing a semiconductorlight-emitting element of this example, at least in the interface sideof the p-side electrode 150 to the second semiconductor layer 140, thevoid 210 can be formed by self-assembly according to migration of silverby high-temperature heat treatment.

That is, by the high-temperature heat treatment of the p-side electrode150, thermal stress is generated by the thermal expansion coefficientdifference between the different kinds of materials, and the stress isconcentrated on the grain boundaries, and in order to relax the stress,the metal atom and the atomic vacancy of the conductive film 151 diffuseand move, and thereby, the void 210 is formed along the gain boundaries.

In this case, for improving reproducibility of formation of size anddensity of the void 210, it is necessary to control the migration ofp-side electrode 150 (conductive film 151).

Therefore, attachment of moisture and/or ionized substance, which hasthe effect of promoting the migration, to the wafer is controlled.

In the producing method of this example, by keeping the wafer in a spacein which the temperature and the humidity are controlled for a certaintime, moisture and/or ionized substance for promoting migration(migration-promoting substance) is attached with good reproducibility. Amethod for keeping the wafer in a thermo-hygrostat chamber in which thetemperature and the humidity can be controlled is also possible. Thespecific condition for attaching the migration-promoting substance ischanged according to, the characteristics of the conductive film 151 andthe semiconductor layer 148 to be used, the treatment conditions of thewafer, and so forth, and therefore, the specific condition isappropriately determined base thereon.

And, in the each of the steps before and after forming the p-sideelectrode 150, attachment in which the migration-promoting substance(moisture and/or ionized substance) is not controlled is prevented asmuch as possible. Specifically, for example, after each of the wettreatment steps before and after forming the p-side electrode 150, rinseby ultrapure water is sufficiently performed, and drying is sufficientlyperformed. Moreover, in the air blow or the spin dryer to be performedafter the rinse, although the moisture on the wafer appears to have beenremoved, slight moisture or wet nagging around the wafer surface isleft, and moreover, if the wafer is heated by a hot plate or an ovenimmediately before forming the conductive film 151 in the state that theresist is formed, the organic solvent evaporates from the resist andadheres to the surface of the semiconductor layer 148, and thereproducibility of the migration of the p-side electrode 150 formedthereon becomes significantly degraded, and therefore, also for thedrying method, the ingenuity is required as described above.

Moreover, as described above the temperature-lowering rate in thehigh-temperature heat treatment and after the heat treatment is set tobe low, formation of the void 210 by the migration is performed withgood reproducibility.

As described above, in the method for producing a semiconductorlight-emitting element of this example, by controlling the attachment ofmoisture and/or ionized substance having the effect for promoting themigration to the wafer and also by setting the temperature-lowering ratein the high-temperature treatment and after the heat treatment to below, the void 210 having a width of the wavelength or less can be formedwith good reproducibility.

The migration-promoting substance includes, for example, water, ionizedsubstance (substance having relatively high ionization tendency andvarious compounds thereof), and various organic substances derived fromthe resist or the like.

Hereinafter, mechanism of formation of the void 210 by the heattreatment will be explained in detail.

FIG. 9 is a schematic view showing behavior of crystal grain in heattreatment in the method for producing a semiconductor light-emittingelement according to the second example of this invention.

As shown in FIG. 9, substance that is easy to migrate such as silvershows such behavior as the surface area becomes the smallest in the heattreatment, similarly to surface tension that is a property of liquid.

That is, when the conductive film 151 (thin film of silver or silveralloy) film-formed on the semiconductor layer 148 is heat-treated, thethermal stress is generated by the thermal expansion coefficientdifference between the different kinds of materials, and the metal atomsmove for trying to relax the stress. In this case, because the metalatoms in the crystal grains 220 attracts each other to try toconcentrate, the metal atoms in the vicinity of the gain boundary 230diffuse and move to the center of the crystal grain 220, and the void210 is generated in the grain boundaries 230.

And, the surface roughness of the conductive film 151 is, for example,about 1.5 nm before the heat treatment, but after the heat treatment,the crystal grains 220 somewhat get moving, and therefore, the surfaceroughness increases to be, for example, about 2.5 nm. When the heattreatment temperature is raised, the diffusion rate of the metal atomsbecomes rapid according to Arrhenius' law, but the stress due to thermalstress becomes small. Moreover, because another equilibration reactionin which the crystal grains 220 are connected one another is alsogenerated, the width of the void 210 and the density of the void 210 inthe plane of the p-side electrode 150 become a local maximal value in acertain heat treatment temperature.

The width of the void 210, and the density and the area ratio in theplane of the p-side electrode 150 can be controlled by the state of themigration-promoting substance (namely, condition of the step for keepingthe wafer for a certain time before the heat treatment, and so forth),the heat treatment (temperature, time, and temperature rising andlowering rates of the heat treatment), type, film thickness, andmultilayer structure of the conductive film 151, and so forth.

If a multilayer structure in which silver or silver alloy that is easyto migrate is used as the p-side electrode 150 at least in the interfaceside to the semiconductor layer 148 as described above, the void 210 canbe formed in the interface of the semiconductor layer 148 side.

As described previously, the optical output is changed corresponding todensity and area ratio of the void 210, and therefore, theabove-described production condition can be changed considering theproductivity and the optical output efficiency.

As described above, by adopting the electrode sintering process(high-temperature heat treatment process) in which silver contained inthe p-side electrode easily migrates, the diffusion reflection region(void 210) can be formed by self-assembly, and the semiconductorlight-emitting element can be realized at low cost.

FIRST COMPARATIVE EXAMPLE

Next, a structure of the semiconductor light-emitting element of a firstcomparative example and the producing method thereof will be explained.

FIG. 10 is a sectional schematic view illustrating a structure of thesemiconductor light-emitting element of the first comparative example.

As shown in FIG. 10, in the semiconductor light-emitting element 91 ofthe first comparative example, the void 210 is not provided in thesecond electrode 150. The structure except for this point is the same asthe semiconductor light-emitting element 11 of the first exampleillustrated in FIG. 4, and the explanation thereof will be omitted.

Hereinafter, the method for producing the semiconductor light-emittingelement 91 of the first comparative example will be explained. In themethod for producing the semiconductor light-emitting element of thefirst comparative example, the steps until forming the semiconductorlayer 148 can be the same as the method for producing the semiconductorlight-emitting element of the second example, and therefore, theproducing method after the steps will be explained.

FIGS. 11A to 11E are schematic views following the steps illustratingthe method for producing the semiconductor light-emitting element of thefirst comparative example.

FIG. 11A is a view of a first step, and FIGS. 11B and 11E are viewsfollowing the preceding views, respectively.

FIG. 11A is an enlarged view of the region 300 in which the SiO₂ film310 is formed on the semiconductor layer.

First as shown in FIG. 11B, similarly to the first example, on thesemiconductor layer 148 on which the SiO₂ film 310 is formed, thelift-off resist 320 is formed in a predetermined pattern, and some ofthe SiO₂ film 310 on the p-type GaN contact layer 146 was removed byammonium fluoride treatment, and moisture on the wafer was blown off byan air blow or a spin dryer or the like.

In this state, as shown in FIG. 11C, a little moisture remains on thewafer surface in the state of being not controlled.

And, as shown in FIG. 11D, by a vacuum deposition apparatus, on theentire wafer, Ag, Pt, and Ti were film-formed in this order at a totalfilm-thickness of 200 nm, and thereby, a conductive film 151 for formingthe p-side electrode 150 was formed.

And, as shown in FIG. 11E, the resist 320 was dissolved by an organicsolvent, and thereby, only the conductive film 151 formed on the resist320 was removed and rinsed by ultrapure water, and then, the wafer wasdried. Thereby, the p-side electrode 150 was formed in the region inwhich the SiO₂ film 310 was removed.

And, then, by using an RTA apparatus, temperature of the wafer wasraised to 350° C. at 5° C./second in a nitrogen atmosphere, and thewafer was subjected to heat treatment for 1 minute in the nitrogenatmosphere at 350° C., and the temperature was lowered to the normaltemperature at 0.5° C./second. Thereby, the semiconductor light-emittingelement 91 of the first comparative example illustrated in FIG. 10 wasformed.

That is, in the method for producing the semiconductor light-emittingelement 91 of the first comparative example, the drying step beforeforming the conductive film 151 for the p-side electrode 150 asillustrated in FIG. 7D and the step of attaching the migration-promotingsubstance as illustrated in FIG. 8C in the producing method of thesecond example of this invention are omitted.

Hereinafter, evaluation results of the semiconductor light-emittingelement 11 of the first example formed as described above and thesemiconductor light-emitting element 91 of the first comparative examplewill be explained.

FIGS. 12A and 12B are scanning electron micrographs illustrating thestructures of the surfaces of the second electrodes of the semiconductorlight-emitting element according to the first example of this inventionand the semiconductor light-emitting element of the first comparativeexample.

That is, FIG. 12A corresponds to the semiconductor light-emittingelement 11 of the first example, and the FIG. 12B corresponds to thesemiconductor light-emitting element 91 of the first comparativeexample.

As shown in FIG. 12B, in the second electrode (p-side electrode) 150 inthe semiconductor light-emitting element 91 of the first comparativeexample, no distinguishing image was confirmed, and the surface statewas the same as the state before the heat treatment. That is, the voidwas not formed in the p-side electrode 150 of the semiconductorlight-emitting element 91. And, in the evaluation of the surfaceroughness by the atom force microscope, the surface roughness was about1.7 nm, which was the same as the surface roughness before the heattreatment.

On the other hand, as shown in FIG. 12A, in the p-side electrode 150 ofthe semiconductor light-emitting element 11, granular image (parts whosebrightness is low in the figure) 291 was observed. For the size of thegranular image 291 in the planar view, the diameter thereof was about0.3 μm on an average. As a result of performing further analysis by ascanning electron microscope or an atomic force microscope, it was foundthat the upper side (opposite surface to the second semiconductor layer120) of the granular image 291 is relatively flat and the surfaceroughness of the surface of the upper side of the part of the granularimage 291 is about 2.6 nm, which is the same as the region except forthe granular image 291, and that the granular image 291 is the void 210formed in the interface of the p-side electrode 150 to the semiconductorlayer 140. And, it was found that the upper side of the void 210 (theopposite side to the second semiconductor layer 140) is capped by thep-side electrode 150.

And, the void 210 was formed in the grain boundaries 230 of the silveralloy of the p-side electrode 150.

In the semiconductor light-emitting element 11 according to thisexample, as the p-side electrode 150, the conductive film 151 composedof Ag, Pt, and Ti is used. By the high-temperature heat treatment, Agand Pt diffused to each other, but the metal layer having titanium asthe main component is left in the surface, and by migration of Ag alloy,the void 210 is formed in the grain boundaries 230.

The area ratio of the void 210 in the plane of the p-side electrode 150was about 0.9%.

The flat region (gray level part of brightness in the figure) 292 havingno void 210 shows an ohmic characteristic and a high efficientmirror-reflection characteristic, and the void 210 shows a diffusereflection characteristic. In the void 210, there is vacuum or anitrogen gas of the heat treatment atmosphere, and the refractionindices of the both cases are thought to be about 1, and therefore, therefraction index difference between the void and the p-type GaN contactlayer 146 is large and the structure easily generates total internalreflection.

Moreover, because there is no light absorber in the void 210, absorptionloss is small by repeating the reflection. Furthermore, in the void 210,it is thought that there is little moisture and little ionizedsubstance, degradation of the p-side electrode 150 can be suppressed andtherefore the reliability is improved.

By these effects, according to the semiconductor light-emitting element11 according to the first example, the semiconductor light-emittingelement with high light taking-out efficiency and high reliability canbe provided.

Third Embodiment

Hereinafter, a third embodiment of this invention will be explained.

FIG. 13 is a sectional schematic view illustrating a structure of thesemiconductor light-emitting element according to a third embodiment ofthis invention.

As shown in FIG. 13, in the semiconductor light-emitting element 30according to the third embodiment of this invention, the void 210 of thesecond electrode (p-side electrode) 150 is provided not only in theinterface to the second semiconductor layer 140 but also continuously tothe opposite surface to the second semiconductor layer 140 of the p-sideelectrode 150. That is, the void 210 is provided so as to pass throughthe layer of the p-side electrode 150 in the film-thickness direction.The semiconductor light-emitting element 30 has the same structure asthe semiconductor light-emitting element 10 according to the firstembodiment illustrated in FIGS. 1A and 1B except for the shape of thevoid 210, and also, the planar structure of the semiconductorlight-emitting element 30 can be the same as the semiconductorlight-emitting element 10, the explanation thereof will be omitted.

As described above, also by the semiconductor light-emitting element 30in which the void 210 is provided so as to pass through the p-sideelectrode 150 continuously in the thickness direction of the p-sideelectrode 150, the light path of the light generated in thelight-emitting layer 130 can be changed by the void 210, and thelight-trapping effect by the total internal reflection in the interfacehaving the refraction index difference can be suppressed, and thesemiconductor light-emitting element with high light taking-outefficiency can be provided.

Also, in the semiconductor light-emitting element 30 of this embodiment,by using the single crystal AlN buffer layer (the first AlN buffer layer122, the second AlN buffer layer 123 of high purity, and the non-dopedGaN buffer layer 124), differently from the low-temperature growth AlNbuffer layer that is amorphous or polycrystalline, the buffer layer isdifficult to become an absorber to the emitted light, and the defects inthe semiconductor layer can be reduced, and the factor causing lightabsorption in the semiconductor layer can be reduced as much aspossible. Thereby, the emitted light can repeat reflection at many timesin the interface between the epitaxial layer (semiconductor layer 148)and the p-side electrode 150, and therefore, the emitted light istrapped in the epitaxial layer (semiconductor layer 148) and easilyaffected by the effect in the 210, and thereby, even if the density orthe area ratio of the void 210 is low, high light taking-out efficiencycan be obtained.

THIRD EXAMPLE

Hereinafter, the method for producing the semiconductor light-emittingelement having this structure will be explained.

The method for producing the semiconductor light-emitting element of thethird example is partial modification of the method for producing thesemiconductor light-emitting element of the second example illustratedin FIGS. 6A to 8D. And, in this case, the heat treatment temperature ofthe p-side electrode 150 is changed to change the density of the void210, and the relation between the void 210 and the optical output wasinvestigated.

FIG. 14A to 14G are schematic sectional views following step sequence ofthe substantial part illustrating the method for producing asemiconductor light-emitting element according to the third example ofthis invention.

FIG. 14A is a view of a first step, and FIGS. 14B and 14G are viewsfollowing the preceding views, respectively.

That is, as shown in FIG. 14A, the SiO₂ film 310 was provided on thesemiconductor layer 148, and then for forming the p-side electrode 150,the patterned lift-off resist 320 was formed on the semiconductor layer148, and some of the SiO₂ film on the p-type GaN contact layer 146 wasremoved by ammonium fluoride treatment.

In this case, as shown in FIG. 14B, in the state that the moisture onthe wafer is merely blown off, a little moisture remains on the wafersurface in the state of being not controlled.

Then, as shown in FIG. 14C, the moisture on the wafer is sufficientlydried and removed.

And, as shown in FIG. 14D, by a vacuum deposition apparatus, on theentire wafer, an Ag monolayer was formed at a film-thickness of 200 nm.

And, as shown in FIG. 14E, the resist 320 was dissolved by an organicsolvent, and thereby, only the conductive film 151 formed on the resist320 was removed and sufficiently rinsed by ultrapure water, and then,the wafer was sufficiently dried on a hot plate at 120° C. Thereby, thep-side electrode 150 was formed in the region in which the SiO₂ film 310was removed.

And, as shown in FIG. 14F, the wafer was kept in a clean room in whichthe temperature and the humidity were controlled to be 25° C.±1° C. and50%±1% respectively for 24 hours, and thereby, a little moisture 330 orionized substance 340 was attached to the surface of the formed p-sideelectrode 150.

And, as shown in FIG. 14G, by using an RTA apparatus, the heat treatmentwas performed for 1 minute in an nitrogen atmosphere by three kinds oftemperatures of 450° C., 700° C., and 800° C., and the temperature waslowered at 5° C./second to the normal temperature, and thereby, the void210 was formed in the interface between the p-type GaN contact layer 146and the p-side electrode 150.

Then, similarly to the second example, the first electrode (n-sideelectrode) 160 was formed in the same method as the second example, andthereby, the semiconductor light-emitting element of this example wasformed.

That is, in the case of the second example, the p-side electrode was Ag,Pt, and Ti, and the heat treatment temperature by RTA was 800° C.However, this example is different in the points that the p-sideelectrode 150 was an Ag monolayer and that the heat treatmenttemperature by RTA was changed to be the three kinds of 450° C., 700°C., and 800° C.

FIG. 15 is a scanning electron micrograph illustrating the structure ofthe surface of the second electrode of the semiconductor light-emittingelement according to the third example of this invention.

That is, FIG. 15 is a photograph of a scanning electron microscopyimaging of the surface of the p-side electrode 150 of the semiconductorlight-emitting element formed at the heat treatment temperature of 800°C.

As shown in FIG. 15, granular images 291 having about a diameter of 0.1μm on an average were observed. As a result of performing furtheranalysis by a scanning electron microscope or an atomic forcemicroscope, it was found that in the grain boundaries 230 of silver, avoid 210 like a hole passing from the surface of the p-side electrode150 to the p-type GaN contact layer 146 was formed. That is, it wasfound that by high-temperature heat treatment, Ag of the p-sideelectrode 150 migrated and the void 210 was formed in the grainboundaries 230.

Hereinafter, the evaluation result of the semiconductor light-emittingelement by the above-described method for producing a semiconductorlight-emitting element according to the first example will be explained.

FIG. 16 is a graphic view illustrating the relation between the heattreatment temperature in the semiconductor light-emitting elementaccording to the third example of this invention and the area ratio ofthe void of the semiconductor light-emitting element.

In FIG. 16, the horizontal axis represents temperature of RTA heattreatment, and the vertical axis represents area ratio of the void 210in the p-side electrode 150.

As shown in FIG. 16, in the semiconductor light-emitting element of thethird example, the area ratios of the void 210 in the plane of p-sideelectrode 150 were 0.5%, 1.2%, 0.8% in the heat treatment temperaturesof 450° C., 700° C., and 800° C., respectively. As described above, thearea ratio of the void 210 indicates a local maximum value in the heattreatment temperature of 700° C.

When the heat treatment temperature is raised, the diffusion rate of themetal atoms by following Arrhenius' law becomes rapid, but the stress bythe thermal stress becomes small. Moreover, because anotherequilibration reaction that the crystal grains 220 bind to one anotheris also generated, the area ratio of the void 210 in the p-sideelectrode 150 indicates a local maximum value in a certain temperatureas described above. In this example, the area ratio of the void 210indicated the local maximum value in the heat treatment temperature of700° C.

FIG. 17 is a graphic view illustrating the relation between the heattreatment temperature and the optical output of the semiconductorlight-emitting element in the semiconductor light-emitting elementaccording to the third example of this invention.

In FIG. 17, the horizontal axis represents temperature of RTA heattreatment, and the vertical axis represents optical output of thesemiconductor light-emitting element. The data that the heat treatmenttemperature in the figure is 350° C. represents the data of thecomparative example in which the void is not formed in the p-sideelectrode 150.

And, this figure illustrates the optical output of the semiconductorlight-emitting element of this example as the relative ratio so that theoptical output of the semiconductor light-emitting element ofcomparative example in which the void 210 is not formed in the p-sideelectrode 150 is 1.

As shown in FIG. 17, it was found that in the semiconductorlight-emitting element of this example, the optical output is largecompared to the comparative example having no void, and that by formingthe void 210, the optical output is improved by about 30% at themaximum.

As described above, according to the semiconductor light-emittingelement of this example, the semiconductor light-emitting element withhigh light taking-out efficiency can be provided.

SECOND AND THIRD COMPARATIVE EXAMPLES

Hereinafter, as the comparative examples, the semiconductorlight-emitting elements of a second comparative example in which thevoid is not formed and a third comparative example in which the hugevoid with bad reproducibility is formed will be explained.

FIGS. 18A to 18E are schematic sectional views following step sequenceof the substantial part illustrating the method for producing asemiconductor light-emitting element of the second comparative example.

FIG. 18A is a view of a first step, and FIGS. 18B to 18E are viewsfollowing the preceding views, respectively.

As shown in FIG. 18B, after the SiO₂ film 310 is formed on thesemiconductor layer 148, a lift-off resist 320 is formed in apredetermined pattern, and some of the SiO₂ film 310 on the p-type GaNcontact layer 146 was removed by ammonium fluoride treatment, andmoisture on the wafer was blown off by an air blow or a spin dryer orthe like.

In this case, as shown in FIG. 18B, in the state that the moisture onthe wafer is merely blown off, a little moisture remains on the wafersurface in the state of being not controlled.

Therefore, then, as shown in FIG. 18C, the moisture on the wafer issufficiently dried and removed.

As shown in FIG. 18D, by a vacuum deposition apparatus, on the entirewafer, a silver monolayer (the conductive film 151) was formed at afilm-thickness of 200 nm, and then, the resist 320 was dissolved by anorganic solvent, and thereby, only the conductive film 151 formed on theresist 320 was removed and sufficiently rinsed by ultrapure water, andthen, the wafer was sufficiently dried on a hot plate at 120° C.Thereby, the p-side electrode 150 was formed in the region in which theSiO₂ film 310 was removed.

And, as shown in FIG. 18E, by using an RTA apparatus, temperature of thewafer was raised to 800° C. at 5° C./second in a nitrogen atmosphere,and the wafer was subjected to heat treatment for 1 minute in thenitrogen atmosphere at 800° C., and the temperature was lowered to thenormal temperature at 0.5° C./second.

That is, in the method for producing the semiconductor light-emittingelement of the second comparative example, the step for attaching themigration-promoting substance illustrated in FIG. 14F in the method forproducing the semiconductor light-emitting element of the third exampleof this invention is omitted.

FIGS. 19A to 19E are schematic sectional views following step sequenceof the substantial part illustrating the method for producing asemiconductor light-emitting element of the second comparative example.

FIG. 19A is a view of a first step, and FIGS. 19B to 19E are viewsfollowing the preceding views, respectively.

As shown in FIG. 19A, after the SiO₂ film 310 is formed on thesemiconductor layer 148, a lift-off resist 320 is formed in apredetermined pattern, and some of the SiO₂ film 310 on the p-type GaNcontact layer 146 was removed by ammonium fluoride treatment, andmoisture on the wafer was blown off by an air blow or a spin dryer orthe like.

In this case, as shown in FIG. 19B, in the state that the moisture onthe wafer is merely blown off, a little moisture remains on the wafersurface in the state of being not controlled.

And, as shown in FIG. 19C, by a vacuum deposition apparatus, on theentire wafer, a silver monolayer (the conductive film 151) was formed ata film-thickness of 200 nm.

And, as shown in FIG. 19D, the resist 320 was dissolved by an organicsolvent, and thereby, only the conductive film 151 formed on the resist320 was removed and sufficiently rinsed by ultrapure water, and then,the wafer was sufficiently dried on a hot plate at 120° C. Thereby, thep-side electrode 150 was formed in the region in which the SiO₂ film 310was removed.

And, as shown in FIG. 19E, by using an RTA apparatus, temperature of thewafer was raised to 800° C. at 5° C./second in a nitrogen atmosphere,and the wafer was subjected to heat treatment for 1 minute in thenitrogen atmosphere at 800° C., and the temperature was lowered to thenormal temperature at 0.5° C./second.

That is, in the method for producing the semiconductor light-emittingelement of the third comparative example, the drying step beforefilm-forming the conductive film 151 for the p-side electrode 150illustrated in FIG. 14C and the step for attaching themigration-promoting substance illustrated in FIG. 14F in the method forproducing the semiconductor light-emitting element of the third exampleof this invention are omitted.

FIGS. 20A and 20B are scanning electron micrographs illustratingstructures of the surfaces of the second electrodes of the semiconductorlight-emitting elements of the second and third comparative examples.

That is, FIG. 20A corresponds to the second comparative example and FIG.20B corresponds to the third comparative example.

As shown in FIG. 20A, in the semiconductor light-emitting element of thesecond comparative example, before forming the conductive film 151 to bethe p-side electrode 150, sufficient drying was performed, and therebythe process for suppressing the migration was performed, and therefore,despite the same electrode structure as the second example and the heattreatment condition of 800° C., the void was not formed at all. Theimage that can be seen in the figure is the grain boundary 230.

On the other hand, as shown in FIG. 20B, in the semiconductorlight-emitting element of the third comparative example, despite thesame electrode structure as the second example and the heat treatmentcondition of 800° C., the size (width) of the void enlarged to about 1μm. Moreover, at a plurality of times, the semiconductor light-emittingelements of the third comparative example were produced by the sameprocess flow, but size and density of the void 210 did not have thereproducibility.

It is thought that in the third comparative example, because theconductive film 151 to be the p-side electrode 150 was formed in thestate of not sufficiently performing drying and the heat treatment wasperformed without sufficiently performing drying after the lift-offprocess, the migration of silver was excessively promoted and the void210 became huge. Moreover, when the drying state was good by accidentdespite the same process flow, the size of the void 210 was suppressed,and consequently, the size of the void could not be controlled.

As shown in the above-described semiconductor light-emitting elements ofthe second comparative example and the third comparative example, whenthe particular treatment such as the drying step before film-forming theconductive film 151 for the p-side electrode 150 or the step forattaching the migration-promoting substance is not performed, the void210 is not formed or the huge void 210 with low reproducibility becomesformed. Therefore, in forming the semiconductor light-emitting elementaccording to this embodiment, the particular treatments such as thedrying step before film-forming the conductive film 151 for the p-sideelectrode 150 and the step for attaching the migration-promotingsubstance are required as explained in the third example.

FOURTH EXAMPLE

Hereinafter, the semiconductor light-emitting element according to thefourth example will be explained.

In the semiconductor light-emitting element (not shown in a figure) ofthis example, the material used for the p-side electrode 150 is changedto Ag and Pt with respect to the semiconductor light-emitting element 30according to the third embodiment explained previously. And, the otherstructure is the same as the semiconductor light-emitting element 30according to the third embodiment, and the explanation thereof will beomitted.

The method for producing the substantial part of the semiconductorlight-emitting element 31 according to this example is as follows.

First, some of the SiO₂ film was removed by ammonium fluoride treatment,and the moisture on the wafer was blown off, a little moisture remainingon the wafer surface was sufficiently dried and removed. And, forforming the p-side electrode 150, a thin film (the conductive film 151)was formed in the order of Ag and Pt at a total film-thickness of 200 nmby a vacuum deposition apparatus on the entire wafer. And, by thelift-off method, the p-side electrode 150 was formed in the region inwhich the SiO₂ film 310 was removed. And, the wafer was kept in a cleanroom in which the temperature and the humidity were controlled to be 25°C.±1° C. and 50%±1% respectively for 24 hours, and thereby, themigration-promoting substance (a little moisture 330 and/or ionizedsubstance 340) was attached. Then, by using an RTA apparatus, the heattreatment was performed for 1 minute in a nitrogen atmosphere of 800°C., and thereby, the void 210 was formed in the p-side electrode 150.That is, by the same condition as the semiconductor light-emittingelement of the third example except for changing the material of theconductive film 151, the semiconductor light-emitting element accordingto this example was produced.

FIG. 21 is a scanning electron micrograph illustrating structure of thesurface of the second electrode of the semiconductor light-emittingelement of the fourth example.

As shown in FIG. 21, in the semiconductor light-emitting element 31according to the fourth example of this invention, granular images 291having a diameter of about 0.2 μm on an average were observed. As aresult of performing further analysis by a scanning electron microscopeor an atomic force microscope, it was found that in the grain boundariesof the silver alloy, a void 210 like a hole passing to the p-type GaNcontact layer 146 was formed. That is, the void 210 passing through thep-side electrode 150 was formed.

By the high-temperature heat treatment, the silver and platinum diffusedto each other, and by the migration of the silver alloy, the void 210was formed in the grain boundary. The area ratio of the void 210 in theplane of the p-side electrode 150 was 2.9%.

Also, in the semiconductor light-emitting element 31 according to thefourth example, by the void 210 having a width of the wavelength of thelight or less provided in the p-side electrode 150, the semiconductorlight-emitting element with high light taking-out efficiency can beprovided.

Fourth Embodiment

FIG. 22 is a sectional schematic view illustrating the structure of thesemiconductor light-emitting element according to the fourth embodimentof this invention.

As shown in FIG. 22, the semiconductor light-emitting element 40according to the fourth embodiment of this invention further includes atransparent electrode 410 provided between the second electrode 150 andthe second semiconductor layer 140.

The structures except for this transparent electrode 410 can be the sameas the semiconductor light-emitting element 30 according to the thirdembodiment illustrated in FIG. 13, and therefore, the explanationthereof will be explained. In the semiconductor light-emitting element40 illustrated in FIG. 22, the second electrode 150 has the void passingthrough the layer of the second electrode 150. However, this inventionis not limited thereto, but it is also possible that the void 210 isformed only in the interface of the second semiconductor layer 140 sideof the second electrode 150 like the semiconductor light-emittingelement 10 illustrated in FIGS. 1A and 1B.

For the transparent electrode 410, a substance having a larger band gapthan the emission wavelength of the light-emitting layer 130 or a metalfilm having a sufficiently thinner film thickness than an inverse numberin the emission wavelength can be used. For the transparent electrode410, for example, nickel, ITO (Indium-tin-oxide), zinc oxide, or thelike can be used.

And, the transparent electrode 410 is electrically in contact with thesecond semiconductor layer 140 and the second electrode 150. Thetransparent electrode 410 has a role of transmitting the light from thelight-emitting layer 130 and reflecting the light by the secondelectrode 150, and therefore, it is preferable that the shape thereof inthe planar view is substantially the same as the second electrode 150.The film thickness of the transparent electrode 410 is not particularlylimited, and for example, can be selected from 1 nm to 500 nm.

FIGS. 23A to 23G are schematic sectional views following step sequenceof the substantial part illustrating the method for producing asemiconductor light-emitting element according to the fourth example ofthis invention.

FIG. 23A is a view of a first step, and FIGS. 23B and 23G are viewsfollowing the preceding views, respectively.

That is, as shown in FIG. 23A, the SiO₂ film 310 is provided on thesemiconductor layer 148, and then for forming the p-side electrode 150,the patterned lift-off resist is formed on the semiconductor layer 148,and some of the SiO₂ film on the p-type GaN contact layer 146 is removedby ammonium fluoride treatment. And, in the region in which the SiO₂film is removed, ITO is formed at a film thickness of 100 nm by using avacuum deposition apparatus, and after the lift-off process, thesintering treatment is performed for one minute in a nitrogen atmosphereof 550° C., and thereby, the transparent electrode 410 is formed, andfurthermore, a patterned lift-off resist 320 is formed on thesemiconductor layer 148.

In this case, as shown in FIG. 23B, in the state that the moisture onthe wafer is merely blown off, a little moisture remains on the wafersurface.

Then, as shown in FIG. 23C, the moisture on the wafer is sufficientlydried and removed.

And, as shown in FIG. 23D, by a vacuum deposition apparatus, on theentire wafer, the conductive film 151 to be the second electrode 150such as an Ag monolayer is formed at a film-thickness of 200 nm.

And, as shown in FIG. 23E, the resist 320 was dissolved by an organicsolvent, and thereby, only the conductive film 151 formed on the resist320 is removed and sufficiently rinsed by ultrapure water, and then, thewafer is sufficiently dried on a hot plate at 120° C. Thereby, thep-side electrode 150 is formed in the region in which the SiO₂ film 310is removed.

And, as shown in FIG. 23F, the wafer is kept in a clean room in whichthe temperature and the humidity are controlled to be 25° C.±1° C. and50%±1% respectively for 24 hours, and thereby, a little moisture 330and/or ionized substance 340 is attached to the surface of the formedp-side electrode 150.

And, as shown in FIG. 23G, by using an RTA apparatus, the heat treatmentis performed for 1 minute in an nitrogen atmosphere of a temperature of550° C., and the temperature was lowered at 5° C./second to the normaltemperature, and thereby, the void 210 is formed in the interfacebetween the p-type GaN contact layer 146 and the p-side electrode 150.

And, similarly as explained previously, the first electrode 160 isformed, and thereby, the semiconductor light-emitting element 40according to this embodiment can be formed.

Also, in the semiconductor light-emitting element 40 of this embodimentfurther having the transparent 410 between the second electrode 150 andthe second semiconductor layer 140 produced as described above, thesemiconductor light-emitting element with high light taking-outefficiency can be provided by the void 210 having an width of thewavelength of the light or less provided in the second electrode 150.

The width of the void 210 and the density and the area ratio in theplane of the p-side electrode 150 can be changed by the heat treatmenttemperature and/or by type, film thickness, and multilayer structure ofthe metal material to be heat-treated at the same time as the conductivefilm 151. However, these conditions that are optimized for improving theoptical output do not necessarily have the optimum combination with theelectrical characteristic. In this case, when the transparent electrode410 is provided between the second electrode 150 and the secondsemiconductor layer 140 and the second electrode 150 functioning as ahigh efficient reflective film is provided through the transparentelectrode 410 like the semiconductor light-emitting element 40 accordingto this embodiment, the optimized conditions for forming the void 210with heavily weighting the optical-output improvement characteristic canbe adopted, and thereby, the semiconductor light-emitting element withhigh light taking-out efficiency that can be more easily produced andthat has higher performance can be provided.

Fifth Embodiment

FIGS. 24A and 24B are schematic views illustrating a structure of thesemiconductor light-emitting element according to the fifth embodimentof this invention.

That is, FIG. 24B is a plan schematic view illustrating the structure ofthe semiconductor light-emitting element according to the fifthembodiment of this invention, and the FIG. 24A is a sectional schematicview of the A-A′ line.

As shown in FIGS. 24A and 24B, the semiconductor light-emitting element50 according to the fifth embodiment of this invention has theabove-described second electrode 150 having the void 210 and a thirdelectrode 155, on the second semiconductor layer 140. And, the thirdelectrode 155 is electrically in contact with the second electrode 150.

Moreover, the third electrode 155 can have a better ohmic property thanthe ohmic property of the second electrode 150.

The position for providing the third electrode 155 is optional as longas being on the second semiconductor layer 140. However, as illustratedin FIGS. 24A and 24B, when the third electrode 155 is provided incontact with the first electrode 160 side of the second electrode 150,the conductive part having high ohmic property can be disposed in theregion opposed to the first electrode 160, and therefore, stableelectric characteristic can be obtained.

The structure except for the third electrode 155 can be the same as thesemiconductor light-emitting element 30 according to the thirdembodiment illustrated in FIG. 13, and therefore, the explanationthereof will be omitted. In the semiconductor light-emitting element 50illustrated in FIGS. 24A and 24B, the second electrode 150 has the void210 passing through the layer of the second electrode 150. However, thisinvention is not limited thereto, but it is also possible that the void210 is formed only in the interface of the second semiconductor layer140 side of the second electrode 150 like the semiconductorlight-emitting element 10 illustrated in FIGS. 1A and 1B.

The semiconductor light-emitting element 50 according to this embodimentcan be produced as follows.

That is, similarly to the method for producing the semiconductorlight-emitting element 30 illustrated in FIGS. 23A to 23G previously,the second electrode 150 (for example, Ag monolayer film having a filmthickness of 200 nm) with a predetermined pattern having the void 210 isformed, and then, for example, an Ag/Pt film for forming the thirdelectrode 155 is formed in a predetermined pattern at a film thicknessof 200 nm, and by using an RTA apparatus, the heat treatment for 1minute in an nitrogen atmosphere of 350, which is one of the conditionsof not generating the void, is performed. Thereby, the void is notgenerated in the third electrode 155, and the ohmic property thereof canbe higher than that of the second electrode.

And, similarly as explained previously, the first electrode 160 isformed, and thereby, the semiconductor light-emitting element 50illustrated in FIGS. 24 and 24B can be obtained.

The width of the void 210 and the density and the area ratio in theplane of the p-side electrode 150 can be changed by the heat treatmenttemperature and/or by type, film thickness, and multilayer structure ofthe metal material to be heat-treated at the same time as the conductivefilm 151. However, these conditions that are optimized for improving theoptical output do not necessarily have the optimum combination with theelectrical characteristic.

Moreover, in the case of the electrode structure for carrying thecurrent in the lateral direction (the direction parallel to each of thelayers) like the above-described semiconductor light-emitting element ofthis embodiment, the current has a tendency of concentrating on the sideof the second electrode 150 opposed to the first electrode 160. Inparticular, the effect appears more significantly as the current densityis more enhanced.

In this case, when the third electrode 155 that is electrically incontact with the side of the second electrode 150 opposed to the firstelectrode 160 and that has a better ohmic characteristic than that ofthe second electrode 150 and that has a high efficient light-reflectivecharacteristic is provided like the semiconductor light-emitting element50 of this embodiment, both of the light taking-out efficiency and theelectrical characteristic can be highly satisfied. That is, variousconditions for the second electrode 150 can be optimized by focusingattention on improving the light taking-out efficiency, and the variousconditions for the third electrode 155 can be optimized by focusingattention on improving the electrical characteristic.

That is, by providing the third electrode with good ohmic property likethe semiconductor light-emitting element 50 of this invention, thesemiconductor light-emitting element with good electrical characteristicand high light taking-out efficiency can be provided.

As the area of the third electrode 155 in the planar view is moreenlarged, the electrical characteristics are more improved, but theenlargement to an extent leads to saturation of the improvement. On theother hand, for improving the light taking-out efficiency, the effectthereof is higher as the area of the second electrode 150 is larger.Considering these effects, by adapting the second electrode 150 and thefirst electrode 160 to the design, the area of the third electrode 155can be appropriately determined.

The semiconductor light-emitting element 50 illustrated in FIGS. 24A and24B has a structure in which the second electrode 150 is first formedand the third electrode 155 is provided so as to cover some of thesecond electrode 150. However, it is also possible to adopt a structurein which the third electrode 155 is first formed and the secondelectrode 150 is provided so as to cover some of the third electrode155. In this case, the temperature of the high-temperature heattreatment of the third electrode 155 can be set to be higher than thetemperature of the high-temperature heat treatment of the secondelectrode 150.

Also, in the semiconductor light-emitting element 50 according to thisembodiment, the transparent electrode may be provided at least in a partbetween the second semiconductor layer 140 and at least any one of thesecond electrode 150 and the third electrode 155.

Sixth Embodiment

FIG. 25 is a sectional schematic view illustrating a structure of thesemiconductor light-emitting element according to a sixth embodiment ofthis invention.

As shown in FIG. 25, in the semiconductor light-emitting element 60according to the sixth embodiment of this invention, a pad 158 isprovided in the surface of the second electrode 150 opposite to thesecond semiconductor layer 140.

The structure except for the pad 158 is the same as the semiconductorlight-emitting element 30 according to the third embodiment illustratedin FIG. 13, and the explanation thereof will be omitted. In thesemiconductor light-emitting element 60 illustrated in FIG. 25, thesecond electrode 150 has the void 210 passing through the layer of thesecond electrode 150. However, this invention is not limited thereto,but it is also possible that the void 210 is formed only in theinterface of the second semiconductor layer 140 side of the secondelectrode 150 like the semiconductor light-emitting element 10illustrated in FIGS. 1A and 1B.

After forming the second electrode 150 having the void 210, the pad 158can be formed by, for example, forming Pt/Au at a film thickness of 800nm so as to cover a part on the second electrode 150 or to cover theentire part containing the side surface of the second electrode 150 andthen patterning the Pt/Au in a predetermined shape. For the patterning,for example, the lift-off method can be used.

For the second electrode 150 side of the pad 158, it is preferable touse high-melting-point material such as not diffusing to the secondelectrode 150. The high-melting-point material include, for example,vanadium (V), chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni),niobium (Ni), molybdenum (Mo), ruthenium (Ru), rhodium (Rh), tantalum(Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), andplatinum (Pt). Rhodium (Rh) or platinum (Pt) is particularly preferable,and has the reflective ratio with respect to the visible light that ishigh to some extent, and therefore, also functions as the reflectivefilm.

By providing the pad 158 like the semiconductor light-emitting element60 according to this embodiment, the bondability of the wire bonding canbe improved, and the die shear strength in formation of gold bump with aball bonder can be improved, and furthermore, this can be applied to theflip-chip mount. Furthermore, by the pad 158, the second electrode 150is separated from the outside air, and degradation of the silver or thesilver alloy can be suppressed, and the reliability thereof is improved.Furthermore, the improvement of the heat release property of thesemiconductor light-emitting element 60 can be expected. This pad 158can also be used as gold (Au) bump. Also, instead of Au, an AuSn bumpcan be formed.

That is, by providing the pad 158 like the semiconductor light-emittingelement 60 according to this embodiment, the semiconductorlight-emitting element with high light taking-out efficiency that can beeasily produced and that has high reliability and that has good heatrelease property can be provided.

Also, in the semiconductor light-emitting element 60 according to thisembodiment, the above-described third electrode 155 in contact with thesecond electrode 150 may be provided, and the transparent electrode maybe provided at least in a part between the second semiconductor layer140 and at least any one of the second electrode 150 and the thirdelectrode 155.

FIG. 26 is a sectional schematic view illustrating another structure ofthe semiconductor light-emitting element according to a sixth embodimentof this invention.

As shown in FIG. 26, in another semiconductor light-emitting element 61according to the sixth embodiment of this invention, a pad 158 isprovided in the surface of the second electrode 150 opposite to thesecond semiconductor layer 140. And, some of the void 210 of the secondelectrode 150 is buried with the conductive material to be the pad 158.

That is, the semiconductor light-emitting element 61 illustrated in FIG.26 has, for example, a structure in which the second electrode 150 hasthe void 210 passing through the layer of the second electrode 150 onthe way of the production and some of the void 210 is buried by thesubsequent formation of the pad 158.

The structure except for the void 210 is the same as the semiconductorlight-emitting element 60 illustrated in FIG. 25, and therefore, theexplanation thereof will be omitted.

And, as shown in FIG. 26, in the semiconductor light-emitting element61, a part 210A out of the void 210 is buried by the pad 158 but thespace remains in the interface of the second semiconductor layer 140. Onthe other hand, in another part 210B of the void 210, the entirety ofthe void is buried with the material to be the pad 158.

In the part 210A of the void in which the space remains in the interfaceof the semiconductor layer 140, the light taking-out efficiency isimproved by the same effect as explained previously.

And, in the part 210B of the void in which the entirety of the void 210is buried, the light taking-out efficiency is improved by the followingeffect.

That is, by using the different conductive materials between the secondelectrode 150 and the pad 158, the difference of the complex refractiveindex between the both can be generated, and thereby, the diffusereflection is generated, and the light taking-out efficiency can beimproved.

The wavelength in a medium is a value of the wavelength in a free spaceof the emitted light divided by the refractive index of the medium andbecomes shorter than the wavelength in a free space. For example, in thecase of the semiconductor light-emitting element 61 according to thisembodiment, when the refractive index of the layer (p-type GaN contactlayer 146) of the second electrode 150 side of the second semiconductorlayer 140 is 2.47 with respect to the emission wavelength of 380 nm, thewavelength in the medium becomes about 150 nm. Therefore, in the case ofburying the void region with another metal (the conductive film to bethe pad 158) like the semiconductor light-emitting element 61, forgenerating effective diffuse reflection, it is desirable that the widthof the void 210 is set to be the same length or less as the wavelengthin the medium.

In the case of the structure in which the void 210 is provided only inthe interface side of the second electrode 150 to the secondsemiconductor layer 140 and the void 210 is passivated by the conductivefilm of the second electrode 150 like the semiconductor light-emittingelement 10 illustrated in FIGS. 1A and 1B, the refractive index in thevoid 210 is about 1 without changing before and after the formation ofthe pad 158, and therefore, it is sufficient that the width of the void210 is almost the same length or less as the wavelength in a free space.

As described above, also in the case that some of the void 210 is buriedwith a different conductive material (metal) from the second electrode150, the diffuse reflection can be generated, and the semiconductorlight-emitting element with high light taking-out efficiency can beprovided.

Also in another semiconductor light-emitting element 61 of thisembodiment, the above-described third electrode 155 in contact with thesecond electrode 150 may be provided, and the transparent electrode maybe provided at least in a part between the second semiconductor layer140 and at least any one of the second electrode 150 and the thirdelectrode 155.

Seventh Embodiment

Next, a seventh embodiment will be explained. The semiconductorlight-emitting element according to this embodiment is a semiconductorlight-emitting element in which the above-described semiconductorlight-emitting element of each of the embodiments and each of theexamples and a fluorescent material are combined.

FIG. 27 is a sectional schematic view illustrating a structure of thesemiconductor light-emitting element according to the seventh embodimentof this invention.

As shown in FIG. 27, the semiconductor light-emitting element 70according to the seventh embodiment of this invention includes, forexample, the semiconductor light-emitting element 30 of the thirdembodiment and a fluorescent material layer 530 that can be excited bythe light emitted in the semiconductor light-emitting element 30 to emita fluorescent light.

That is, as shown in FIG. 27, a reflective film 520 is provided in theinner surface of the container 510 made of ceramics or the like. Thereflective film 520 is provided so as to be divided into the reflectivefilm 521 on the bottom surface of the container 510 and the reflectivefilm 522 on the side surface of the container 510. For the reflectivefilm 520, for example, aluminum or the like can be used.

And, on the reflective film 521 of the bottom surface of the container510, the semiconductor light-emitting element 30 is disposed through asubmount 524. On the semiconductor light-emitting element 30, a goldbump 528 is formed by a ball bonder, and the semiconductorlight-emitting element 30 is fixed to the submount 524. It is alsopossible that without using the gold bump 528, the semiconductorlight-emitting element 30 is fixed to the submount 524.

For example, adhesion by an adhesive agent or solder or the like can beused for the fixation of the semiconductor light-emitting element 30,the submount 524, and the reflection film 520.

On the surface of the semiconductor light-emitting element 30 side ofthe submount 524, patterned electrodes are formed so as to be insulatedwith respect to the second electrode (p-side electrode) 150 and thefirst electrode (n-side electrode) 160 of the semiconductorlight-emitting element 30, and the respective patterned electrodes areconnected to the electrodes (not shown in figure) provided in thecontainer 510 side, with the bonding wires 526. The connections areperformed in parts between the reflective film 522 of the side surfaceand the reflective film 521 of the bottom surface.

And, the fluorescent material layer 530 is provided so as to cover thesemiconductor light-emitting element 30 and the bonding wires 526. Inthe semiconductor light-emitting element 70 illustrated in FIG. 27, asthe fluorescent material layer 530, a first fluorescent material layer531 containing a red fluorescent material and a second fluorescentmaterial layer 532 provided on the first fluorescent material layer 531and containing a blue, green or yellow fluorescent material areprovided. On these fluorescent material layers 530, for example, a lid512 made of silicon resin is provided.

The first fluorescent material layer 531 includes a resin and a redfluorescent material dispersed in the resin. For the red fluorescentmaterial, for example, Y₂O₃, YVO₄, Y₂(P,V)O₄ or the like can be used asthe base material, and trivalent Eu (Eu³⁺) is contained therein as theactivation substance. That is, Y₂O₃:Eu³⁺, YVO₄:Eu³⁺, or the like can beused as the red fluorescent material. The concentration of Eu³⁺ can be1% to 10% by molar concentration. As the base material of the redfluorescent material, as well as Y₂O₃ or YVO₄, LaOS or Y₂(P,V)O₄ or thelike can be used. Moreover, as well as Eu³⁺, Mn⁴⁺, or the like can beutilized. In particular, by adding a small amount of Bi with thetrivalent Eu to the base material of YVO₄, the absorption of 380 nmincreases, and therefore, the light-emitting efficiency can be enhanced.Moreover, as the resin, for example, silicon resin or the like can beused.

Moreover, the second fluorescent material layer 532 includes a resin anda fluorescent material that is at least any one of blue, green, andyellow and that is dispersed in the resin. For example, the fluorescentmaterial in which the blue fluorescent material and the greenfluorescent material are combined may be used, or the fluorescentmaterial in which the blue fluorescent material and the yellowfluorescent material are combined may be used, or the fluorescentmaterial in which the blue fluorescent material, the green fluorescentmaterial, and the yellow fluorescent material are combined may be used.

For the blue fluorescent material, for example, (Sr,Ca)₁₀(PO₄)₆Ci₂:Eu²⁺or BaMg₂Al₁₆O₂₇:Eu²⁺ or the like can be used.

For the green fluorescent material, for example, Y₂SiO₅:Ce³⁺,Tb³⁺ inwhich the trivalent Tb is the emission center can be used. In this case,because the energy is transfer from Ce ion to Tb ion, the excitationefficiency is improved. For the green fluorescent material, for example,Sr₄Al₁₄O₂₅:Eu²⁺ or the like can be used.

For the yellow fluorescent material, for example, Y₃Al₅:Ce³⁺ or the likecan be used.

Moreover, for the resin, for example, silicon resin or the like can beused.

In particular, the trivalent Tb indicates sharp emission in the vicinityof 550 nm, in which the visibility becomes the maximum, and therefore,when the trivalent Tb is combined with the sharp red emission of Eu, theemission efficiency is significantly improved.

By the semiconductor light-emitting element 70 according to thisembodiment, the ultraviolet light of 380 nm generated from thesemiconductor light-emitting element 30 is emitted to the substrate sideof the semiconductor light-emitting element 30, and the reflection inthe reflective films 521, 522 is also utilized, and thereby, theabove-described fluorescent materials contained in the respectivefluorescent material layers can be efficiently excited.

For example, in the above-described fluorescent material having theemission center of the trivalent Eu or the like contained in the firstfluorescent material layer 531, the light is converted into a lighthaving the wavelength distribution of the vicinity of 620 nm, andthereby the red visible light can be efficiently obtained.

Moreover, the blue, green, or yellow fluorescent material contained inthe second fluorescent material layer 532 is efficiently excited, andthereby, the blue, green, or yellow visible light can be efficientlyobtained.

As the mixed colors thereof, a white light and lights with the othervarious colors can be obtained with high efficiency and good colorrendering properties.

In the above description, the example in which the semiconductorlight-emitting element 30 according to the third embodiment is used hasbeen presented, but this invention is not limited thereto, and theabove-described semiconductor light-emitting elements 10, 11, 40, 50,60, and 61 according to the embodiments and the examples can be used.

Next, the method for producing the semiconductor light-emitting elementaccording to this embodiment will be explained.

The steps for producing the semiconductor light-emitting element 30 arethe same as explained previously.

And, first, the metal film to be the reflective film, is formed on theinner surface of the container 510 by, for example, a sputtering method,and the metal film is patterned to form the reflective films 521, 522 inthe bottom surface and the side surface of the container 510,respectively.

And, on the semiconductor light-emitting element 30, the gold bumps 528are formed by a ball bonder. And, on the submount 524 having theelectrodes patterned for the second electrode (p-side electrode) 150 andthe first electrode (n-side electrode) 160 of the semiconductorlight-emitting element 30, the semiconductor light-emitting element 30is fixed, and the submount 524 is disposed and fixed onto the reflectivefilm 521 of the bottom surface of the container 510. For the fixation,adhesion by an adhesive agent or solder or the like can be used.Moreover, it is also possible that without using the gold bump 528 bythe ball bonder, the semiconductor light-emitting element 30 is directlyfixed onto the submount 524.

Next, the first electrode 160 and the second electrode 150 (not shown)on the submount 524 are connected to the electrodes (not shown) providedin the container 510 side, respectively, with bonding wires 526.Furthermore, the first fluorescent material layer 531 is formed so as tocover the semiconductor light-emitting element 30 or the bonding wires526, and the second fluorescent material layer 532 is formed on thefirst fluorescent material layer 531. For the respective methods forforming the fluorescent material layers, for example, a method ofdropping each of the fluorescent materials dispersed in the resinmaterial mixtures and then performing thermal polymerization by heattreatment to harden the resin can be used. When the resin materialmixture containing each of the fluorescent materials is dropped and thenleft to stand for a while and then hardened, the fine particles of eachof the fluorescent materials are precipitated and the fine particles canbe localized to the lower part of each of the layers of the firstfluorescent material layer 531 and the second fluorescent material layer532, and thereby, the emission efficiency of each of the fluorescentmaterials can be appropriately controlled. Then, the lid 512 is providedon the fluorescent material layer, and thereby, the semiconductorlight-emitting element 70 according to this embodiment, namely, whiteLED is produced. As described above, by the produced semiconductorlight-emitting element 70 of this embodiment, the semiconductorlight-emitting element with high light taking-out efficiency that cangenerate various colors with high efficiency can be provided.

In each of the above-described embodiments, the example in which thefirst semiconductor layer 120 is an n-type semiconductor layer and thesecond semiconductor layer 140 is a p-type semiconductor layer has beenpresented. However, this invention is not limited thereto, and theconductivity types can be inverted.

As described above, the embodiments of this invention has been explainedwith reference to the specific examples. However, this invention is notlimited to these specific examples. For example, the specific structuresof each of the components composing the semiconductor light-emittingelement and the method for producing the same, such as shape, size,material, arrangement relation, and crystal growth process of each ofthe components such as the semiconductor multilayer film, the metalfilm, and the dielectric film, are included in the scope of thisinvention as long as the invention can be similarly carried out byperforming appropriate selection from the known range by those skilledin the art and the same effect can be obtained.

Moreover, combinations of two or more components of each of the specificexamples in the technically possible range are included in the scope ofthis invention as long as including the spirit of this invention.

In addition, all of the semiconductor light-emitting elements and themethods for producing the same which can be carried out withappropriately design-modified by those skilled in the art based on thesemiconductor light-emitting element and the method for producing thesame that have been described as the embodiments of this invention alsobelong to the scope of this invention as long as including the spirit ofthis invention.

In addition, it is understood that in the range of the idea of thisinvention, various modified examples and changed examples can beachieved by those skilled in the art and that the modified examples andthe changed examples also belong to the scope of this invention.

In this specification, “nitride semiconductor” includes all of thesemiconductors having the compositions in which the composition ratiosx, y, and z are changed in the respective ranges in the chemical formulaof B_(x)In_(y)Al_(z)Ga_(1−x−y−z)N (0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z≦1).Furthermore, in the above-described chemical formula, the semiconductorfurther containing a group V element except for N (nitrogen) or thesemiconductor further containing any one of various dopants to be addedfor controlling the conductivity type and so forth is also included inthe “nitride semiconductor”.

1. A semiconductor light-emitting element comprising: a firstsemiconductor layer; a second semiconductor layer; a light-emittinglayer provided between the first semiconductor layer and the secondsemiconductor layer; a first electrode connected to the firstsemiconductor layer; and a second electrode provided on the secondsemiconductor layer, wherein a side of the second electrode facing tothe second semiconductor layer is composed of at least any one of silverand silver alloy, wherein the second electrode has a void having a widthof emission wavelength or less of the light-emitting layer in a plane ofthe second electrode facing to the second semiconductor layer, andwherein the void is provided in an interface of the second electrode tothe second semiconductor layer and provided so as to pass through thethickness direction of the second electrode.
 2. The element according toclaim 1, wherein the void is formed by migration according tohigh-temperature heat treatment of silver contained in the secondelectrode.
 3. The element according to claim 1, wherein the firstsemiconductor layer, the second semiconductor layer and thelight-emitting layer are formed on a sapphire substrate.
 4. The elementaccording to claim 1, wherein the first semiconductor layer, the secondsemiconductor layer and the light-emitting layer are made ofAl_(x)Ga_(1−x−y)In_(y)N (x≧0, y≧0, x+y≦1).
 5. The element according toclaim 1, wherein the first semiconductor layer has n-type conductivityand the second semiconductor layer has p-type conductivity.
 6. Theelement according to claim 1, wherein the second electrode is a silvermonolayer film.
 7. The element according to claim 1, further comprisinga third electrode, the third electrode: being provided on the secondsemiconductor layer, being in contact with the second electrode, andhaving a higher ohmic property than an ohmic property of the secondelectrode with respect to the second semiconductor layer.
 8. The elementaccording to claim 1, further comprising a fluorescent material havingan emission center of trivalent Eu and excited by a light with theemission wavelength to emit a red light, the first semiconductor layer,the second semiconductor layer and the light-emitting layer being madeof semiconductor nitride, the emission wavelength of the light-emittinglayer being 370 nm to 400 nm.
 9. The element according to claim 1,further comprising a transparent conductive film being provided betweenthe second semiconductor layer and the second electrode and transmittinga light from the light-emitting layer.
 10. The element according toclaim 9, wherein the transparent conductive film is made of a materialhaving a larger band gap than an energy of photon at an emissionwavelength of the light-emitting layer.
 11. The element according toclaim 9, wherein a film thickness of the transparent conductive film isthinner than an inverse number of an absorption coefficient in anemission wavelength of the light-emitting layer.
 12. The elementaccording to claim 9, wherein the transparent conductive film containsat least one of nickel, indium tin oxide, and zinc oxide.
 13. Theelement according to claim 1, wherein the first semiconductor layer, thesecond semiconductor layer and the light-emitting layer are formed on asapphire substrate via a single crystal aluminum nitride layer.
 14. Theelement according to claim 13, wherein in the sapphire substrate side ofthe single crystal aluminum nitride layer, a region having a highercarbon concentration than that of the inside of the single crystalaluminum nitride layer is provided.
 15. A semiconductor light-emittingelement comprising: a first semiconductor layer; a second semiconductorlayer; a light-emitting layer provided between the first semiconductorlayer and the second semiconductor layer; a first electrode connected tothe first semiconductor layer; and a second electrode provided on thesecond semiconductor layer, wherein a side of the second electrodefacing to the second semiconductor layer is composed of at least any oneof silver and silver alloy, wherein the second electrode has a voidhaving a width of emission wavelength or less of the light-emittinglayer in a plane of the second electrode facing to the secondsemiconductor layer, and wherein the void is provided in an interface ofthe second electrode to the second semiconductor layer and in aninterface of the second electrode opposite to the second semiconductorlayer.
 16. A semiconductor light-emitting element comprising: a firstsemiconductor layer; a second semiconductor layer; a light-emittinglayer provided between the first semiconductor layer and the secondsemiconductor layer; a first electrode connected to the firstsemiconductor layer; and a second electrode provided on the secondsemiconductor layer, wherein a side of the second electrode facing tothe second semiconductor layer is composed of at least any one of silverand silver alloy, wherein the second electrode has a void having a widthof emission wavelength or less of the light-emitting layer in a plane ofthe second electrode facing to the second semiconductor layer, andwherein the void is provided in the interface of the second electrode tothe second semiconductor layer and in a layer of the second electrode.17. A semiconductor light-emitting element comprising: a firstsemiconductor layer; a second semiconductor layer; a light-emittinglayer provided between the first semiconductor layer and the secondsemiconductor layer; a first electrode connected to the firstsemiconductor layer; and a second electrode provided on the secondsemiconductor layer, wherein a side of the second electrode facing tothe second semiconductor layer is composed of at least any one of silverand silver alloy, wherein the second electrode has a void having a widthof emission wavelength or less of the light-emitting layer in a plane ofthe second electrode facing to the second semiconductor layer, andwherein the second electrode is a silver monolayer film.
 18. Asemiconductor light-emitting element comprising: a first semiconductorlayer; a second semiconductor layer; a light-emitting layer providedbetween the first semiconductor layer and the second semiconductorlayer; a first electrode connected to the first semiconductor layer; asecond electrode provided on the second semiconductor layer; and a thirdelectrode being provided on a second semiconductor layer, being incontact with the second electrode and having a higher ohmic propertythan an ohmic property of the second electrode with respect to thesecond semiconductor layer, wherein a side of the second electrodefacing to the second semiconductor layer is composed of at least any oneof silver and silver alloy, and wherein the second electrode has a voidhaving a width of emission wavelength or less of the light-emittinglayer in a plane of the second electrode facing to the secondsemiconductor layer.
 19. A semiconductor light-emitting elementcomprising: a first semiconductor layer; a second semiconductor layer; alight-emitting layer provided between the first semiconductor layer andthe second semiconductor layer; a first electrode connected to the firstsemiconductor layer; and a second electrode provided on the secondsemiconductor layer, wherein a side of the second electrode facing tothe second semiconductor layer is composed of at least any one of silverand silver alloy, wherein the second electrode has a void having a widthof emission wavelength or less of the light-emitting layer in a plane ofthe second electrode facing to the second semiconductor layer, whereinthe first semiconductor layer, the second semiconductor layer and thelight-emitting layer are formed on a sapphire substrate via a singlecrystal aluminum nitride layer, and wherein in the sapphire substrateside of the single crystal aluminum nitride layer, a region having ahigher carbon concentration than that of the inside of the singlecrystal aluminum nitride layer is provided.
 20. A semiconductorlight-emitting element comprising: a first semiconductor layer; a secondsemiconductor layer; a light-emitting layer provided between the firstsemiconductor layer and the second semiconductor layer; a firstelectrode connected to the first semiconductor layer; a second electrodeprovided on the second semiconductor layer; and a fluorescent materialhaving an emission center of trivalent Eu and excited by a light withthe emission wavelength to emit a red light, the first semiconductorlayer, the second semiconductor layer and the light-emitting layer beingmade of semiconductor nitride, the emission wavelength of thelight-emitting layer being 370 nm to 400 nm, wherein a side of thesecond electrode facing to the second semiconductor layer is composed ofat least any one of silver and silver alloy, and wherein the secondelectrode has a void having a width of emission wavelength or less ofthe light-emitting layer in a plane of the second electrode facing tothe second semiconductor layer.